This invention relates to processes for treating alkaline effluent solutions obtained from lithographic printing plate processing, systems for controlling such processes, and methods of controlling such processes. More particularly, this invention relates to processes for treating such alkaline effluent solutions by neutralizing the alkaline effluent solution in such a manner as to obtain a discharge solution which is readily handled and may be disposed of in an environmentally acceptable manner without further processing, systems for controlling such processes, and methods of controlling such processes.
Certain industrial processes generate effluent solutions and process streams which may be highly acidic or alkaline, depending upon the particular industrial process involved. For example, the processing of lithographic printing plates involves the use of at least one developer solution which is basic (i.e. having a pH above 7.0) and at least one finishing solution, gum solution, pre-bake solution or combinations thereof which are acidic (i.e. having a pH below 7.0). Consequently, such processing typically causes the generation of highly acidic and alkaline effluent solutions or process streams that must be further processed or treated before discharge into the environment, or they must be treated as hazardous waste, which adds additional cost and complexity to the overall process.
More particularly, the lithographic printing process typically employs the use of a highly alkaline developer solution having a pH greater than about 12.5 (for example, MX-1710, SILVERSTAR, and GOLDSTAR developers, having pH values of 13.0-13.5, as manufactured by Kodak Polychrome Graphics of Norwalk, Conn.), and highly acidic finishing, gum and pre-bake solutions having a pH less than about 5.0 (for example, MX 1612-1 and POLYMATIC finishers, having pH values of below 2.0, as manufactured by Kodak Polychrome Graphics of Norwalk, Conn.). The highly alkaline developer solutions are required, for example, to completely solubilize non-image portions of the exposed plates. The highly acidic solutions are required, for example, to completely convert the processed non-image portions of baked plates to uniformly hydrophilic surfaces. These solutions generate effluent or process streams which are classified as hazardous materials under the federal Resource Conservation and Recovery Act (RCRA) and applicable regulations. Thus, the discharge of these highly alkaline and acidic effluent streams into the environment is ordinarily impermissible without further treatment. Alternatives such as dilution of the effluent streams with water is often impermissible, and in any event is ordinarily costly and requires large quantities of fresh water, which is often not available. In addition, it has been found that simply neutralizing the highly alkaline effluent stream with the highly acidic effluent stream or with a separate acidic solution often causes the formation of unacceptable gels, sludge or precipitates.
Accordingly, it would be desirable to neutralize the alkaline effluent solution in such a manner as to avoid the formation of unacceptable gels, sludge, or precipitates. It is one object of this invention to provide a process for achieving such neutralization. It is one feature of this invention that the alkaline effluent stream is neutralized using at least one acidic solution to obtain a neutralized effluent stream, and that an additional aqueous solution or stream is used in the neutralization process to advantageously avoid the formation of unacceptable gels, sludge, or precipitates, thereby obtaining a neutralized discharge stream which may be discharged to the environment. It is another object of this invention to provide a control system for such a neutralization process. It is yet another object of this invention to provide a method of controlling such a process.